In recent years, X-ray CT apparatuses using a photon counting detector have been developed. Photon counting detectors individually count light derived from X-rays that have passed through the subject, unlike integral detectors used in X-ray CT apparatuses in related art. For this reason, X-ray CT apparatuses using a photon counting detector are capable of reconstructing X-ray CT images with a high signal per noise (SN) ratio. In addition, photon counting enables identification of substance using difference in K absorption edge, because photon counting enables imaging from X-ray output of a single type divided into a plurality of energy components.